1. Field of the Invention
The present invention relates to a slicing method and, more particularly, to a slicing method for a rapid prototyping apparatus.
2. Description of Related Art
A smart discontinuous slicing method is a slicing method applied to three-dimensional rapid prototyping (3DRP). This method can greatly improve the slicing speed. In addition, this method also can avoid connection errors of slicing outlines, which are generated when discontinuous planes of an object exist during the slicing treatment. Hence, correct slicing outlines can also be generated, when the object with the discontinuous planes is sliced based on this method.
FIG. 1A is a perspective view of a conventional arrangement of grids. As shown in FIG. 1A, eight grids, named A to H, are shown. Two cut points 12 are generated when each grid intersects with a slicing plane 11. The cut points in each grid is determined to be a start cut point or an end cut point in an anti-clockwise direction. In addition, the cut point locating in a path with a downward direction is defined as a start cut point, and a cut point locating in a path with an upward direction is defined as an end cut point. A cut line connecting two cut points is a slicing outline of the slicing plane 11 in the grids A-H. Hence, a set of all cut lines, which are the lines that the slicing plane 11 intersects with the grids A-H, forms a slicing outline of the object in the slicing plane 11, as shown in FIG. 1B.
According to the conventional slicing method, a topology relationship is used to establish the relationship between grids. FIG. 2 is a process diagram showing a conventional slicing method generally used in a three-dimensional rapid prototyping (3DRP) system. According to the conventional slicing method, data of cut points, which are generated from a slicing plane 11 intersecting with grids A-H, are first accessed (step S21), as shown in FIG. 2 (also accompanied with FIG. 1A). Then, the following relationship between the grids is established based on the topology relationship (step S22):
The grid next to the grid A is the gird B, the grid next to the grid B is the grid C, the grid next to the grid C is the grid D, the grid next to the grid D is the grid E, the grid next to the grid E is the grid F, the grid next to the grid F is the grid G, the grid next to the grid G is the grid H, and the grid next to the grid H is the grid A.
The connection of the cut lines starts from the cut line of the grid A, and the cut line of the grid A connects to the cut line of the grid B. Next, the cut lines connects to those of the grids C, the grids D . . . and to the grids H. The grid next to the grid H is the grid A, so the connection of the cut lines ends in the cut line of the grid H. After the aforementioned process, all the cut lines in this connection can form a slicing outline, as shown in FIG. 1B (step S23).
In general, the topology relationship is used in the conventional slicing method, so the formation of the slicing outline is accomplished through the connection relationship between grids. However, the order for inputting the grids is not defined in the file, which is input into the three-dimensional rapid prototyping system. Hence, the grids are not arranged in order, so there is no order in the cut points and the cut line of the grids. Therefore, a large amount of calculation is required during the process for forming the connection relationship between grids and finding the connection outline. This large amount of calculation may cause the slicing speed decreased, and the performance efficiency of the slicing software may also be reduced.
In addition, according to the slicing method applied with the topology relationship, the slicing outline is formed by the lines connecting between the cut points during the process for forming the outline. The next grid connected to the present grid is sequentially found through the topology relationship, until the next grid is the start grid. The line connecting all the start cut points of all the grids is the slicing outline. However, a problem may arise during the process for forming the slicing outline. It is that the end cut point may connect to the start cut point when the connection between the cut points is completed.
FIG. 3A is a perspective view showing the connection between cut points in a discontinuous plane of an object when a conventional topology relationship is applied, FIG. 3B is a perspective view showing an actual slicing outline of the discontinuous plane, and FIG. 3C is a perspective view showing an error in the slicing outline when the topology relationship is applied. As shown in FIG. 3A, a connection between cut points in a discontinuous plane is shown, and there is no grid next to the grid that the cut point I exists therein. Hence, the actual slicing outline of the discontinuous plane should be that shown in FIG. 3B.
According to the conventional method for connecting the cut points through the topology relationship, the process for forming the slicing outline is mainly divided into three cycles. The first cycle starts from the cut point I, but the first cycle immediately ends because there is no grid next to the grid that the cut point I exists therein. Next, the second cycle starts from the cut point J. Then, the cut point K, the cut point L, the cut point M, the cut point I are sequentially found through the topology relationship, and these cut points connect one by one. There is no grid next to the grid that the cut point I exists therein, so the end cut point I connects to the start cut point J, and the second cycle ends. The third cycle starts from the cut point N. Then the cut point O, the cut point J, the cut point K, the cut point L, the cut point M, the cut point I are sequentially found through the topology relationship, and these cut points connect one by one. There is no grid next to the grid that the cut point I exists therein, so the end cut point I connects to the start cut point N, and the third cycle ends. During the process for forming the slicing outline by use of the conventional method, the end cut point connects to the start cut point when the connection between the cut points ends. Hence, when the conventional slicing method is used, an error in the slicing outline shown in FIG. 3C may be generated compared to the actual slicing outline shown in FIG. 3B, i.e. the end cut point I spontaneously connects to the start cut point J, and the end cut point I also connects to the start cut point N.
Actually, the conventional slicing method applied with the topology relationship in an imperfect connection relationship between grids. More specifically, the grid A only connects to the grid B, and the grid B only connects to the grid C. Hence, the grids have to be found one by one during the process for forming the slicing outline, i.e. the grid B is found from the grid A, and the grid C only can be found from the grid B. When there is a discontinuous plane, the connection between planes cannot be performed well anymore, so the topology relationship is no longer suitable. Therefore, the conventional slicing method cannot be used for processing discontinuous planes of an object. In addition, it cannot be ensured that there are not any discontinuous planes in the file, which is input into the three-dimensional rapid prototyping system. Hence, the conventional slicing method generally used in the art cannot fully satisfy the requirement for the three-dimensional rapid prototyping system.
Therefore, it is desirable to provide a slicing method for a rapid prototyping apparatus, which can solve the aforementioned problems that the performance efficiency of slicing software is low and the conventional method cannot be used for processing discontinuous planes of an object.